In preliminary work we have characterized two different genetic (autosomal recessive) disorders of human biotin metabolism. In the present proposal we extend our studies of defects in human biotin metabolism, and address certain questions of mechanism and pathophysiology in biotin-dependent genetic diseases. We shall identify and characterize mutants in biotin transport, and utilize a rat animal system to study biotin transport in the central nervous system. We shall exploit certain unique properties of the mutant cells to study the regulation of acetyl CoA carboxylase, a rate-limiting enzyme in mammalian fatty acid synthesis, and the coordinate regulation of the enzymes mediating fatty acid synthesis. These mechanistic studies will complement investigations relating distortions in fatty acid metabolism to aspects of the pathophysiology of the disease states.